| Because of the high content of nutrients and moisture,large yellow croakers were extremely easy to spoil during storage.Biogenic amines were low molecular weight nitrogenous compounds,which were produced through free amino acid decarboxylation reaction under the action of microorganism,and excessive accumulation of biogenic amines might cause poison to human.Some specific spoilage organisms(SSOs)could play a leading role in the process of fish spoilage.According to previous researches,Shewanella baltica was the SSO of refrigerated storage large yellow croakers.Quorum sensing(QS)system was a kind of information communication mechanism among bacterials,many bacterials used it to regulate the expression of related genes for the effect of spoilage.The research about how to inhibit food spoilage by inhibiting quorum sensing has become a focus of attention.Therefore,this work studied on large yellow croakers,investigated dynamic changes of biogenic amines and other quality indexs during storage.Then we chose S.baltica,to study the relationship of growth and decline between quorum sensing and biogenic amines.Furthermore,the ability of anthocyanins in inhibiting quorum sensing and spoilage of S.baltica was evaluated.The main results were as follows:1.Large yellow croakers were stored at 4 ℃ and 25 ℃,respectively,to measure their biogenic amines,trimethylamine(TMA),total viable count(TVC),pH and total volatile basic nitrogen(TVB-N).In addition,the correlation analysis and corresponding linear regression equations were also studied between the biogenic amines and other quality indexes.The results indicated that the storage temperature had significant influence on the quality of large yellow croakers.The rate of quality decreased significantly faster with the higher storage temperature.The results showed that TVC exceeded the threshold in related standard under 25 ℃ and 4 ℃ for 18 h and 6 d,respectively.TVB-N exceeded the threshold in related standard under 25 ℃and 4 ℃ for 36 h and 10 d,respectively.SPSS regression analysis revealed that putrescine(PUT)and cadaverine(CAD)were related to the other quality indexes significantly,with R2 of 0.915 and 0.766,respectively.Above all,these equations could reliably describe the dynamic changes between characteristic biogenic amines and other quality indexes in cultured large yellow croakers during storage.Furthermore,prediction models of PUT and CAD established by multiple linear regression equation were also verified.2.The GC-MS method was developed for simultaneous quantifying two kinds of signal molecules(eight AHLs and four DKPs).The characteristic ions were determined by mass spectrometry,and equations of linear regression,limit of detection,limit of quantitation and recovery rate were determined.Six strains of S.baltica were cultured by shaking under refrigeration in sterile fish juice,to analysis the dynamic changes of signal moleculars and biogenic amines during growth by GC-MS-SIM and HPLC.The results showed that these six strains just produced two kinds of DKPs(cyclo-(L-Pro-L-Leu)and cyclo-(L-Pro-L-Phe))and two kinds of biogenic amines(PUT and CAD).The contents of these DKPs and PUT were significantly positive correlated:they all increased upon the mid to late exponential phase,and then declined,with the highest content at the third day.However,the content of CAD increased slowly in the beginning and became faster when the highest content of signal molecular reached.3.The effects of anthocyanins on quorum sensing and biogenic amines in S.baltica were studied.The results showed that the minimal inhibitory concentration of anthocyanins from blueberries and purple sweet potatos were 2 mg/mL and 6 mg/mL,respectively.Then the effects of ornithine decarboxylase and the contents of signal moleculars and PUT by anthocyanins within the minimal inhibitory concentration were tested,the results showed that the inhibition of cyclo-(L-Pro-L-Leu)by 1.5 and 2 mg/mL anthocyanins from blueberries were 35.1%and 55.2%,and the inhibition of cyclo-(L-Pro-L-Phe)were 35.1%and 55.2%,respectively.The inhibition of cyclo-(L-Pro-L-Leu)by 4 and 6 mg/mL anthocyanins from purple sweet potatos were 23.3%and 38%,and the inhibition of cyclo-(L-Pro-L-Phe)were 18.6%and 31.8%,respectively.However,there was no degradation of DKPs by anthocyanins.Moreover,the inhibition were observed by adding 1,1.5 and 2 mg/mL anthocyanins from blueberries(14.0%,36.1%and 94.4%),or 4 and 6 mg/mL anthocyanins from purple sweet potatos(57.8%,64.5%).Exposure to anthocyanins was also found to be associated with significantly inhibition of the expression of ODC gene by RT-qPCR,the relevant inhibitory rates were 23.2%to 88.1%and 17.0-83.8%by anthocyanins from blueberries and purple sweet potatos,respectively.This study illuminated the dynamic changes of biogenic amines in large yellow croakers during storage and relations between signal moleculars and biogenic amines in S.baltica,providing theoretical basis for the predicting large yellow croakers quality during storage.The selected anthocyanines could be a potential and novel preservative in preservation of aquatic products. |
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